Let's listen now to something President Trump said back in May to supporters at a rally in Tennessee.

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PRESIDENT DONALD TRUMP: And this is why we call the bloodthirsty MS-13 gang members exactly the name that I used last week. What was the name?

UNIDENTIFIED CROWD: Animals.

TRUMP: Animals.

KELLY: Our Code Switch team has a series called Word Watch where they unpack the history behind controversial phrases and words. Today NPR's Shereen Marisol Meraji takes on animal.

SHEREEN MARISOL MERAJI, BYLINE: I've been talking to a lot of people about the word animal since the president made headlines last month for using it. The experts - a neuroscientist, sociolinguist, a philosophy professor and historian Ibram X. Kendi.

IBRAM X KENDI: I think it's critical for first and foremost people in our time to recognize the seriousness of what this language can do, connecting it to the violence that has already occurred in this country.

MERAJI: The violence of slavery, when black people were consistently referred to as beasts.

KENDI: To justify mass murdering and kidnapping of these people.

MERAJI: The violence that came after abolition in the form of lynchings when black men were depicted as ferocious animals out to rape and devour white women. Native Americans were called savages, wolves, lice, their children nits, says David Livingstone Smith. He's a philosophy professor who wrote "Less Than Human: Why We Demean, Enslave, And Exterminate Others."

DAVID LIVINGSTONE SMITH: So, yes, Native Americans - dehumanization was a very, very, very, important feature of the bloody history of this nation. You know, all nations are born in violence, but we Americans have a very difficult time coming to terms with the truth.

MERAJI: More truth - devils, the word used to describe people of Japanese descent before internment during World War II. No dogs, no negroes, no Mexicans, read signs in the windows of businesses across the southwest in the 1950s. And that's the short list. Sociolinguist Otto Santa Ana is compiling a list of his own with help from his students at UCLA. They've been reviewing President Trump's language about immigrants starting from the time he declared his candidacy.

OTTO SANTA ANA: There are hundreds and hundreds of examples of the language of immigrants. There's only a handful that speak to immigrants as humans.

MERAJI: Santa Ana says the president consistently characterizes people migrating from Latin America as illegals and criminal aliens. But study after study show immigrants are less likely to commit crimes than people born in the U.S. The child of Guatemalan immigrants, Kimberly Ceron, is one of the students who spent long hours helping Santa Ana comb through Trump's speeches and tweets.

KIMBERLY CERON: I was disheartened, really, to use American as my identity. Am I a part of this nation? Because clearly you don't think I am.

MERAJI: Joe Concha, a media reporter for The Hill, says President Trump uses informal language, and the media's made too much of these animal references, allowing hyperbolic comparisons to language used during slavery or the Holocaust.

JOE CONCHA: When President Trump compares MS-13 to animals, they are. They really are. And if anybody but Trump says it, no one even blinks twice. Didn't Hillary Clinton once call gang members - oh, boy...

MERAJI: Super predators.

CONCHA: I don't remember. Yeah. Yeah. Exactly.

MERAJI: People did give Clinton heat for that during her presidential bid. But this does touch on something I heard from all the experts I spoke with. Everyone's susceptible to using dehumanizing language and being misled by it. A neuroscientist told me our brains are prewired to attribute negative things to outside groups. So when you hear an MS-13 gang member's an animal, you're susceptible to ascribe those traits to their entire ethnic group. Another thing these experts agreed on - now's the time to take heed and brush up on history. Shereen Marisol Meraji, NPR News. Transcript provided by NPR, Copyright NPR.